Dials, Automatic No. 21

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TELECOMMUNICATIONS INSTRUCTION
C MARKETING - INSTALLATION
3 Internal
M0017
Issue 1, Sept 1971

DIALS, AUTOMATIC No. 21

General
Dials, Automatic No. 21CA (colour) have been introduced in matching colours for use, without extra charge, on Telephones Nos. 706, 710 etc. These telephones have an outer number ring with letters and figures (Label No. 355) and consequently letters and figures are not required on the dial. The letter 'C' in the title indicates that the dial, having neither figures nor letters on the number ring, is common to all automatic systems. First issues of Telephones No. 706 will carry Dials, Automatic No. 12FA but telephones with Dials, Automatic No. 21CA should become available during 1960. Dials, Automatic No. 21LA, Black may be issued in lieu of Dials, Automatic No. 12LA for use on pre 700-type telephones. The letter 'L,' in the title indicates that it includes a number ring bearing figures and letters.

Dials, Automatic Nos. 13 to 20 inclusive will continue to be available until superseding types are announced.

Front view	Rear view
Side view	Mechanism close up

Description
The mechanism is essentially the same as that of the Dial, Automatic No. 12 except that it is mounted on a steel base-.plate attached to a black moulding which forms the body. The material of the pulsing contacts has been changed to Palladium in an effort to prevent high-resistance contact troubles which have occurred on earlier dials. The 'number ring', Label No. 388 (colour), is blank and is held by a retaining spring which locates on two pillars. The finger plate is formed from rigid P.V.C. sheet, and the label protector is moulded in cleardolymethyl methacrylate. The label protector snaps into position in the finger plate and is held by three pips which are equally spaced around the periphery.

The Dial, Automatic No. 21LA, Black is identical with the Dial, Automatic No. 21CA, Black except that it has a Label No. 389 (number ring with letters and figures) instead of a Label No. 386, Black.

COLOURS
Details of colours are shown in Table 1.

TABLE 1

Note: green and grey Labels No. 388, which are darker than the green and grey finger plates, match the colour o the telephone handsets; the finger plates match the colour of the telephone covers.

Removal of label protector
The label protector must not be released by levering at the edge. The edge consists of a thin lip which will break easily. Warning notices are being included in the dials bought under the first contracts, and all staff who will be concerned with the dials should be instructed in the correct method of removal of the label protector. These warning notices should be removed when the dial centre label is fitted.

The easiest method of removal is to use an Extractor No. 29 which is a rubber suction disk with a finger grip. This item [Small Stores, Rate Book Section 5 (T-B)] should be requisitioned from the Supplies Dept. and issued from Section Stock one to each installation and maintenance officer concerned. Unit of issue from the Supplies Dept. is 50. The Extractor No. 29 can be released from the label Protector by lifting one edge of the rubber with the finger nail.

An alternative method of removing the label protector is to insert a Screwdriver No. 1 radially between the finger plate and the number ring at the 13 o'clock position on the dial. The screwdriver will then enter a slot in the finger plate and, by turning the screwdriver beneath the pip in a thin metal plate which is under the label protector, the protector will be ejected. Care must be taken to ensure that the end of the screwdriver is under the metal plate and not between the plate and the label protector. It is advisable to hold two fingers over the protector to restrain it during ejection. It is always advisable when replacing the protector to locate it so that its three Dips are clear of the slot provided for the screwdriver, otherwise subsequent removal might prove difficult.

Dial centre labels
These have been prepared specially for the Dial Auto No. 21...  They have been coded Label No. 386... and should be requisitioned in the same manner as for Labels No. 160...  The one colour label (upper half grey with white lettering, lower half white with black lettering) is suitable for all colours of dial.

Label No. 386A is for use in automatic areas with "999" facilities.  Label No. 386B is for use in automatic areas with "0" facilities. When putting the label into the dial, care should be taken to ensure that its centre line is horizontal.

If delay in receiving Labels No. 366... should prejudice the installation of Telephones No. 706 or 710 fitted with Dials, Automatic, No. 21CA, Labels No. 160... may be used.  The appropriate Label No. 160 ... should continue to be used for installations where Labels No. 386A-B are unsuitable.  Care should be taken to fit the labels with the printing horizontal.

Maintenance
As with earlier dials work on the mechanism is not permitted in subscribers' premises.  The general instructions in Automatic, B 5002 will apply, except that it should be remembered that the reference to coloured dials will not apply to Dials, Automatic, No. 21.  The items which may be changed at subscribers' premises are as follows:-

Finger stop - Part No. 1/DST/19 (Stop, finger)

Label protector - Part No. 1/DPR/5 (Protector, label)

Finger plate - Part No. 1/DPL/2018 (colour) (Plate, finger)

Retaining spring - Part No. 1/DSP/1482 (Spring, retaining, label) for number ring

Number ring - Label No. 368 (colour) or Label No. 389.

A1 Pulse Wheel - Part No. 1/DWH/38 (non-replaceable in the field)

NOTE:- on 700-type telephones the dial cord is provided with spade tags so that it is necessary only to loosen the dial screws to release the cord. Spade tags are also being introduced on other dial cords.

If it becomes necessary to change a Dial, Automatic, No. 21... at a subscribers' premises and a new dial of the correct colour is not readily available, it will generally be possible to use the mechanism of a new Dial, Automatic, No. 21... of another colour, together with the coloured parts of the old dial, provided the latter are in good condition.

Addendum
Around 1968 the GPO decided to drop letters on dials as the UK went STD.  The coloured dial was also dropped in favour of a clear plastic finger plate.  The dial label was coloured "Antique Silver" with black numbers. The dial was called the Dial, Automatic No. 21FA Clear.

As the finger plate was moulded in one piece there was no slot provided in which to insert a screwdriver, to remove the label cover.  A rubber extractor was introduced called an "Extractor No. 29" which effectively was a rubber sucker.  Selotape stuck firmly to the cover and then pulled sharply away from the dial will also normally remove the label cover.

Terminal Connections

Drawings - 92526/1, 92526/2 and 92526/3 (No. 21FA clear).

Dial Fingerplate Labels

Dial Types

Last revised: February 26, 2023